Some of my slabs keep coming loose?

[uptown47]

Hi all,

I have slabs at the top and bottom of my garden. The bottom ones are rock solid but the top ones keep coming loose. I've included a picture of one that came away completely the other day when my daughter stood on the edge of it (very nearly an injury - although her face was priceless!). They've been down 2 years now and the builder has been back 3 times to re-fix them and I don't want to keep bothering him about them.

So I thought I'd ask for advice about how to fix them down - permanently!

I remember asking him last time how he did it and he said he used PVA?. I also noticed that for the "grout" (not sure if that's the right word for the stuff in-between slabs?) he used some stuff that he just sprinkled into the gaps.

I found this similar thread - https://www.diynot.com/diy/threads/patio-slabs-not-sticking.521782/ which talks about "wetting and SBRing" the back of the slabs?

Could someone explain in layman terms the best way to fix these down and to re-grout them?

A big thanks for any help you can give me on this. If I can get advice on how to do it properly then I'll just lift all the loose ones and re-do them all properly one weekend.

 

[^woody^]

• Remove all mortar from around the edge.
  
• Brush away all loose mortar and dust from the base.
  
• Dampen the base and the back of the slab.
• Mix neat cement with a capful of PVA or SBR and water into a creamy grout. Not too runny. About 1/2 a litre volume for that size slab in the photo.
• You won't have much time once mixed before it starts to harden.
• Pour the grout onto the base to a depth of about 5mm.
• You won't like this bit, but then imagine the English flag and form some channels like the cross - about 50mm wide
• Place the slab down and then twist it or slide it a little to get it down to the right level. This is the important bit as this actually makes the bond. Dont bang it down.
  
• Position it evenly then leave it for a day to set.
• Then point up with a mortar mix to match the rest of the pointing - 4:1 sharp sand and semi-dry mix.

I've assumed a 5mm deep grout will be about right, but check this first and adjust as necessary, as you won't want to be lifting the slab after to add more or remove some grout.

If the base mortar is loose, then chop that up and use a 3:1 [soft builders sand] mortar mix instead of grout, but a bit wetter than the pointing mix. Everything else will be the same as above.

 

[uptown47]

Woody, thanks very much for your detailed reply. That was just what I was after.

I don't mind the English flag reference - I'm originally from Burnley but it made me chuckle!

Thanks again for taking the time to write all that. I'll follow it to the letter.

Cheers

 

[uptown47]

Hi Woody

I just wanted to quickly thank you again for your excellent instructions.

I tackled the job over the weekend and the slabs seem well and truly fixed down now!

Will see how they get on over the winter but all looking good so far.

Thanks again for all your help.

 

[noseall]

I would never over-sail slab onto a wall, especially a curved wall. The differential movement alone is a big risk, never mind the problems associated with tipping piddly cuts on the edge and the visible scarring from a grinder cuts.

This is how we do it...

Wave3

• noseall
• 22 May 2017

Wave1

• noseall
• 22 May 2017

Pat12

• noseall
• 17 Sep 2016

 

[stuart45]

I've started doing them like that after seeing one of your pics some time ago, and wouldn't go back to the old way now.

 

[uptown47]

I would never over-sail slab onto a wall, especially a curved wall. The differential movement alone is a big risk, never mind the problems associated with tipping piddly cuts on the edge and the visible scarring from a grinder cuts.

This is how we do it...

Those pictures look lovely. A great finish. I didn't do our slabs, a guy came and did them for me but I really like your finish. Thanks for the pics.